Two dose regimens were assessed in this study. Stage 1 comprised 2 dose cohorts. In Cohort 1, the first 6 participants were to receive blinatumomab in a dose-escalating manner: 9 µg/day for the first week, followed by 28 µg/day for the second week, then 112 µg/day for the remaining 6 weeks of treatment during Cycle 1. In Cohort 2, the next 6 participants enrolled were to receive a constant dose of 112 µg/day blinatumomab. Before the initiation of stage 2, a pre-planned data monitoring committee (DMC) meeting was held to assess the safety profile of Cohort 1 and Cohort 2. The dosing regimen with the more favorable benefit-risk profile was to be selected for Cohort 3.